A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800 s, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been suggested. Actually, electrical toothbrushes or electrical razors, which are frequently used in daily life, are charged based on the principle of electromagnetic induction. The electromagnetic induction refers to a phenomenon in which voltage is induced so that current flows when a magnetic field is varied around a conductor. Although the commercialization of the electromagnetic induction technology has been rapidly progressed around small-size devices, the power transmission distance thereof is short.
Until now, wireless energy transmission schemes include a remote telecommunication technology based on magnetic resonance and a short wave radio frequency in addition to the electromagnetic induction.
Recently, among wireless power transmitting technologies, an energy transmitting scheme employing electromagnetic induction and resonance has been widely used.
In a wireless power transmission system employing the electromagnetic induction and resonance, since an electrical signal formed between a transmitter and a receiver is wirelessly transmitted through a coil, a user can easily charge power in an electronic appliance such as a portable appliance.
However, in the conventional power transmission process, since various frequency bands are used in the transmitter, the receiver may not be sufficiently charged with power when the frequency used in the transmitter differs from that used in the receiver.
In addition, the receiver must use a plurality of coils in order to cover various frequency bands used in the transmitter.
The related art is disclosed in Korean Unexamined Patent Publication No. 10-2006-0058735 titled “Variable inductor for integrated circuit and printed circuit board”.